QUINIDINE SULPHATE TABLETS
(and dosage form):
QUINIDINE SULPHATE TABLETS
Tablets containing 200 mg and 300 mg Quinidine Sulphate.
A 6.2 Cardiac Depressants.
Quinidine is a cardiac depressant; it depresses the restorative metabolism of the heart muscle. Its most valuable action is to lengthen the refractory period of the muscle, i.e. the period of time following each contraction during which the muscle will not respond to a stimulus with another contraction, to 50 per cent or more above the normal. Both the atria and the ventricles ere similarly affected hence, the excitability of heart muscle is decreased by quinidine.
Secondly, the conduction of the excitation wave (stimulus to contract) through both the myocardium and the conduction bundles of the heart is decreased. To a lesser degree, vagal tone, which normally has an inhibiting action on the heart, is decreased but this opposite action is usually minimal compared to the first and second mentioned actions. Decreased contractility of muscle is the third action in order of clinical importance. The rate of contraction of the normal heart is slowed as a result of the increase in refractory period of the sinoatrial node, which normally initiates the excitation wave and this action is not prevented by full doses of atropine; the atrioventricular node is similarly affected. In the normal heart an increase in systolic output (stroke volume) results because secondary to the slower rate there is a longer period of time for filling of the ventricle during diastole. In the decompensated heart however, increased systolic output may not occur and it may actually be decreased as a result of the decreased contractility of the myocardium. In atrial fibrillation the excitation wave (circus movement) follows an irregular and inconstant path around the atrium. Quinidine acts by prolonging the refractory period of the atrial muscle so that no excitable fibres are available to carry the stimulus; the atrium becomes quiet and the sino-atrial node again becomes the normal pace-maker of the atrium as a whole.
For the abolition of certain cardiac arrhythmias. These include atrial fibrillation, atrial flutter, paroxysmal supraventricular and ventricular tachycardia and premature systoles.
It should not be given to hypersensitive patients or patients with a history of thrombocytopenic purpura associated with previous quinidine administration. It is contra-indicated in patients with acute infection, complete heart block or extensive myocardial disease such as valvular disease, auricular fibrillation of long standing, congestive heart failure, cardiac enlargement, mitral stenosis, recent coronary occlusion or a history of embolism.
DOSAGE AND DIRECTIONS FOR USE:
In the prophylaxis of cardiac arrhythmia:
One tablet three times a day.
In the treatment of atrial fibrillation
One to two tablets every 2 to 4 hours to a total dose of ten tablets daily.
SIDE-EFFECTS AND SPECIAL PRECAUTIONS:
Quinidine must be used with special caution in the presence of digitalis intoxication. Previous digitalisation may reduce the sensitivity of the heart to quinidine.
Side-effects include hypersensitivity reactions such as tinnitus, vertigo, visual disturbances, headache, skin eruptions, vomiting, cramps and diarrhoea.
Other serious forms of hypersensitivity are manifested by respiratory depression and arrest cyanosis and a precipitous fall in blood pressure, vascular collapse, and thrombocytopenic purpura. Quinidine may enhance the effects of coumarin anticoagulants and of some skeletal muscle relaxants.
KNOWN SYMPTOMS OF OVERDOSAGE AND PARTICULARS OF ITS TREATMENT:
Quinidine is cumulative in action; the effects of overdosage may include cinchonism, auriculoventricular block, extrasystoles, ventricular tachycardia, cardiac standstill and ventricular fibrillation.
Treatment should be supportive and symptomatic. Elimination may be assisted by acidification of the urine and ensuring an adequate fluid balance.
200 mg Plain white biconvex tablets with a diameter of 8,71 mm.
300 mg Plain white biconvex tablets with a diameter of 10,31 mm.
200 mg Packs of 25, 100 and 500 tablets.
300 mg Packs of 25 and 100 tablets.
Store below 25°C.
KEEP OUT OF REACH OF CHILDREN.
200 mg G2852 (Act 101/1965)
300 mg G2853 (Act 101/1965).
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